Enhanced Forward Osmosis Desalination with a Hybrid Ionic Liquid/Hydrogel Thermoresponsive Draw Agent System

Abstract

Forward osmosis (FO) has emerged as a new technology for desalination and exhibits potentials for applications where reverse osmosis is incapable or uneconomical for treating streams with high salinity or fouling propensity. However, most of current draw agents in FO are salts and difficult to be recycled cost- and energy-effectively. In this work, we demonstrate a new and facile approach to efficiently recover water from the FO process with enhanced water purity by using a binary ion liquid/hydrogel system. The hybrid ion liquid/hydrogel draw solution system demonstrated in this work synergistically leverages the thermoresponsive properties of both the ionic liquid (IL) and hydrogel to improve the overall FO performance. Our findings corroborate that the hydrogel mitigates the water flux decline of the IL as the draw agent and provide a ready route to contiguously and effectively regenerate water from the FO process. Such a route allows for an efficient recovery of water from the draw solute/water mixture with enhanced water purity, compared with conventional thermal treating of lower critical solution temperature IL draw solute/water. Furthermore, hydrogels can be used in a continuous and readily recyclable process to recover water without heating the entire draw solute/water mixture. Our design principles open the door to use low-grade/waste heat or solar energy to regenerate draw agents and potentially reduce energy in the FO process considerably.

Phase separation of an ionic liquid mixture assisted by a temperature gradient

“…The main binary system under investigation is a mixture of MilliQ water with the ionic liquid tetrabutylphosphonium trifluoroacetate (P 4444 CF 3 CO 2 ) [42,43] already used in different applications [7,8,10], at an IL mass fraction of 25% (separation temperature T sep = 31 o C). This system is known as a Lower Critical Solution Temperature (LCST) binary solution, i.e.…”

“…Last decade, temperature-responsive binary systems made of ionic liquids (IL) and water have shown promising applications such as in metal and rare-earth extraction [1,2], protein stabilisation [3,4], catalytic synthesis [5,6], forward osmosis water desalination [7][8][9] and low grade heat valorization [10,11]. Those techniques are built on the reversible phase separation of the system with temperature loops.…”

Thermocapillary instability of an ionic liquid-water mixture in a temperature gradient

“…Since the 2010s, thermoresponsive binary systems made of water and ionic liquids (IL) have proved useful for several applications such as protein stabilisation [1][2][3], catalytic synthesis [4], metal and rare-earth extraction [5][6][7], forward osmosis water desalination [8][9][10] and low grade heat valorization [11,12]. For all these techniques the temperature is used as a control parameter to trigger the phase separation and recover on demand the IL-rich phase of interest.…”

Quaternary Ammonium-Based Ionosilica Hydrogels as Draw Solutes in Forward Osmosis

“…Some recent investigations have therefore focused instead on polyelectrolytes [ 14 ] and poly(ionic liquids) [ 15 ] as draw solutes, allowing for simpler recovery and regeneration procedures. In this context, the use of polymer hydrogels was also considered [ 16 , 17 , 18 ]. Most of the studied hydrogels are based on organic polymers such as polyacrylates, poly(acrylamides), poly(N-isopropylacrylamide) (PNIPAM) or polystryrene sulfonates.…”

“…Most of the studied hydrogels are based on organic polymers such as polyacrylates, poly(acrylamides), poly(N-isopropylacrylamide) (PNIPAM) or polystryrene sulfonates. These systems appeared as stimuli-responsive systems allowing easy recovery via thermal responsiveness [ 16 , 18 ]. Hydrogels therefore combine good performance in generating high osmotic pressure and easy regeneration [ 18 ].…”